I. Field
The present disclosure relates generally to circuits, and more specifically to an amplifier suitable for wireless communication and other applications.
II. Background
Amplifiers are commonly used in various electronics devices to provide signal amplification. Furthermore, different types of amplifiers are available for different uses. For example, a wireless device may include a transmitter and a receiver for bi-directional communication, and the transmitter may utilize a power amplifier (PA) and the receiver may utilize a low noise amplifier (LNA) and a variable gain amplifier (VGA).
An LNA is commonly used in a receiver to amplify a low-amplitude signal received via a communication channel. The LNA is often the first active circuit encountered by the received signal and hence has a large impact on the performance of the receiver in several key areas. First, the LNA has a large influence on the overall noise figure of the receiver since the noise of the LNA is injected directly into the received signal and the noise of subsequent stages is effectively reduced by the gain of the LNA. Second, the linearity of the LNA has a large influence on both the design of subsequent stages in the receiver and the receiver performance. The LNA input signal typically includes various undesired signal components that may come from external interfering sources and leakage from a co-located transmitter. Nonlinearity in the LNA causes the undesired signal components to mix and generate cross modulation distortion (XMD) that may fall within the desired signal bandwidth. The amplitude of the cross modulation distortion is determined by the amount of nonlinearity in the LNA. The cross modulation distortion component that falls within the desired signal bandwidth acts as noise that degrades the signal-to-noise ratio (SNR) of the desired signal. The degradation in SNR caused by LNA nonlinearity impacts the design of (and often places more stringent requirements on) subsequent stages in order to meet the overall SNR specification for the receiver. Therefore, having a more linear LNA can alleviate the performance requirements for other stages, which may result in lower power consumption and smaller circuit area for the receiver.
There is therefore a need in the art for an amplifier having good linearity and noise performance.